Economic grid support from variable renewables

In September 2014, a consortium of research institutes, led by the European Wind Energy Association and supported by the Intelligent Energy Europe programme, published the final results of their study on the feasibility of providing grid support with variable renewable energy sources for electricity. The objective of the study was to investigate whether wind power and photovoltaics are capable ofproviding ancillary services such as frequency support, voltage support and system restoration services in order to support an electricity grid with large shares of renewable generation. The goal of the study is to provide technical and economic guidelines in order to develop a market design which supports the economic and efficient participation of wind power and photovoltaics in ancillary services.

The potential participation of renewable generation in ancillary services is put forward as an inevitable element in the discussion on how to facilitate renewable integration into the system. Firstly, renewable energy sources fundamentally change the system needs for ancillary services due to their variable nature. Secondly, they gradually replace conventional generation technologies which still remain the main supplier of these services. And thirdly, there technical characteristics do allow the participation in ancillary services, often with similar characteristics as the conventional power plants.

The study shows that future needs for ancillary services are likely to increase. The variable nature and limited predictability will require additional reserve capacity for real-time balancing reasons. Furthermore, the replacement of conventional sources of reactive power and voltage control will require the procurement of voltage related services from alternative sources. Although the trend is clear, the exact needs depend strongly on local power system conditions. Specific attention is to be directed towards the distribution system needs, facing an increasing share distributed energy resources.

The report confirms that wind power already meets most technical requirements of ancillary service participation. Remaining challenges are mainly related to communication issues and monitoring the availability of the service. Particularly the last element can be seen as a key element for TSOs requiring high reliability standards when contracting network services. Standardisation and harmonization of procurement procedures are therefore put forward as key elements. Similar conclusions are drawn for photovoltaics which may however face additional challenges due to their small and distributed nature. In contrast, the economic feasibility is seen as a more fundamental barrier as frequency control services result in elevated operational costs, while participation in voltage control results in additional capital expenditures.

Specific attention is directed towards the market and regulatory framework which should ensure a correct remuneration in order to facilitate a voluntary participation. Mandatory provision is usually not a cost-efficient approach, and a market based approach stimulates the procurement of services from power plants with the lowest cost. It is important to pursue a technology neutral market design which also allows future technologies such as storage or demand response to compete with conventional and renewable power on these markets for ancillary services. This may require adaptations of the market framework. For instance, product definitions such as separate up- and downward bidding, confidence intervals and aggregated bids are elements which may facilitate new technologies such as renewable generators to participate in ancillary services. Specific attention is to be paid towards the interaction between the distribution and transmission level in order to meet the ancillary service needs of the distribution system, as well as the potential delivery of grid supporting services sourced from the distribution level.

> More information: http://www.reservices-project.eu/